Nanoceria dissolution at acidic pH by breaking off the catalytic loop.

This manuscript proves the reproducibility and robustness of cerium oxide nanoparticles, nanoceria, employed as a chemical reagent with oxidizing capacity (as an electron sink) at acidic pH. Unlike nanoceria multi-enzyme-mimetic capabilities at neutral or high pH, nanoceria can behave as a stoichiometric reagent at low pH where insoluble Ce 4+ ions transform into soluble Ce 3+ in the nanocrystal that finally dissolves. This behaviour can be interpreted as enzyme-like when nanoceria is in excess with respect to the substrate. Under these conditions, the Ce 3+ /Ce 4+ ratio in the NPs can easily be estimated by titration with ferrocyanide. This procedure could become a rapid assessment tool for evaluating nanoceria capacity in liquid environments.